Sandwich structure

ABSTRACT

A sandwich structure with an outer cover layer, inner cover layer, core layer, and pins extending through the core layer. The sandwich structure has a large core thickness resistant to crack formation and to detachment of the cover layers from the core layer. An anchor layer is between the outer and inner cover layers and divides the core layer, at least in areas, into an outer core layer section and inner core layer section. An outer group of pins extends through the outer core layer section and an inner group of pins extends through the inner core layer section. The outer group pins are connected to the anchor layer with their first end and to the outer cover layer with their opposite second end, and the inner group pins are connected to the anchor layer with their first end and to the inner cover layer with their opposite second end.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Patent Application No. 102015 111 936.6 filed Jul. 22, 2015, the entire disclosure of which isincorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to a sandwich structure, in particular toa pin-reinforced sandwich structure with a large core thickness, and toan aircraft with such a sandwich structure. The sandwich structure isconstructed, in particular, shell-shaped or plate-shaped, wherein it canalso have curves or curvatures.

BACKGROUND

The sandwich structure comprises an outer cover layer, an inner coverlayer disposed opposite the outer cover layer in a thickness direction,and a core layer which, as viewed in the thickness direction, isdisposed between the outer and the inner cover layers and connects them.The designations “outer cover layer” and “inner cover layer” are not inprinciple meant to restrict the positions of the cover layers to aninner side and an outer side, but can just as well be understood to mean“front cover layer” and “back cover layer” or “first cover layer” and“second cover layer”. The sandwich structure furthermore comprises aplurality of pins that extend between the outer cover layer and theinner cover layer, through the core layer. The outer cover layer and theinner cover layer, as well as the pins, are preferably made of a fiberor fibrous composite material, in particular CFRP or GFRP. The corelayer is preferably formed from foam material, such aspolymethacrylimide (PMI).

Such sandwich structures are known from the prior art, for example fromWO 2012/010305 A1. The purpose of the pins therein is to prevent or stopcrack formation in the core layer as well as detachment or delaminationof the cover layers from the core layer. The pins are usually introducedinto the core layer through needles provided for this purpose. Forstability reasons and because of friction between the core layer and theneedles during the introduction of the pins, the length of the needles,and thus the length of the pins, is limited to about 90 mm. This lengthlimit of about 90 mm is related to a particular density of the materialof the core layer and, in the case of a change of this density, it canalso deviate considerably from about 90 mm. Because the pins must extendfrom one cover layer to the opposite cover layer in order to preventdetachment of the cover layers from the core layer, the thickness of thecore layer, and of the entire sandwich structure, is likewise limited inthis manner to a maximum of about 90 mm due to the limited length of thepins. However, because it may be necessary or advantageous to providecore thicknesses considerably greater than about 90 mm for variousapplications of the sandwich structure (such as, for example, inairplane construction) in which applications high shear forces must betransmitted, at present it is not readily possible to also reinforcesuch sandwich structures with large thicknesses with pins. In otherwords, it is either impossible or else extremely difficult tomanufacture pin-reinforced sandwich structures that also have large corethicknesses.

SUMMARY

Thus, an object of the present disclosure is to provide a sandwichstructure with a large core thickness that is particularly resistant tocrack formation in the core layer as well as to detachment of the coverlayers from the core layer.

This object is achieved in that an anchor layer is provided between theouter and the inner cover layers. The anchor layer extends transversely,preferably perpendicularly, to the thickness direction and divides thecore layer, at least in areas, into an outer core layer section orportion in abutment with the outer cover layer and into an inner corelayer section or portion in abutment with the inner cover layer. Thismeans that the outer core layer section is situated between the anchorlayer and the outer cover layer, and that the inner core layer sectionis situated between the anchor layer and the inner cover layer. In thisregard, the anchor layer can extend, in a plane perpendicular to thethickness direction, either through the entire sandwich structure orjust through an area of the sandwich structure. Furthermore, an outergroup of pins extends through the outer core layer section and an innergroup of pins extends through the inner core layer section. The pins ofthe outer group are connected to the anchor layer with a first end andto the outer cover layer with an opposite second end. The pins of theinner group are connected to the anchor layer with a first end and tothe inner cover layer with an opposite second end. The pins in this casecan be connected to the anchor layer and to the cover layers in such away that they project or extend into these layers or penetrate theselayers and are thereby fixed or secured therein.

In this manner, an intermediate layer is formed by the anchor layerbetween the cover layers, in which intermediate layer the pins can beanchored with their first ends such that they only need to span half ofthe thickness or a portion of the thickness of the sandwich structurefrom one of the cover layers to the anchor layer, rather than having toextend across the entire thickness of the sandwich structure from theouter cover layer to the inner cover layer. The core layer is thusdivided into an outer and an inner core layer section or portion, eachof which can be spanned separately by pins. In this manner, an inner aswell as an outer core layer section, each having a thickness of about 90mm, can be spanned with pins having a length of about 90 mm, therebymaking it possible to also reinforce with pins sandwich structureshaving a core layer which has a thickness of up to about 180 mm. Suchsandwich structures can be used, in particular, in the aircraft sector,for example as pressure bulkheads or as wing shells in the area of thewing root. However, they can also be used in other sectors, such as onrotor blades of wind power plants, in trains, or on pressure tanks orcontainers.

In a preferred embodiment, the outer cover layer, the inner cover layer,the anchor layer, and the pins are formed with each other in monolithicfashion from a fiber or fibrous composite material, in particular fromCFRP or GFRP. The cover layers, the anchor layer, and the pins arepreferably cured together with each other. In this manner the coverlayers, the anchor layer, and the pins jointly form a monolithicframework for the sandwich structure, such that loads can be transferredparticularly effectively and crack formation in the core layer as wellas detachments or delaminations of the cover layers can be prevented.

In a further preferred embodiment, the anchor layer is monolithicallyjoined on its layer border or edge to the outer cover layer and/or tothe inner cover layer. In this manner, the anchor layer is fixed at itslayer border or edge and thus stabilized.

In this regard, it is particularly preferred if the sandwich structurecomprises a peripheral or edge area at which the cover layers aremonolithically joined to one another. At the peripheral area of thesandwich structure, the anchor layer is thus monolithically joined withits layer border or edge to the outer and inner cover layers. At itslayer border or edge, the anchor layer is thus clamped between the outerand inner cover layers in the peripheral area of the sandwich structure.The anchor layer is thereby further stabilized. The peripheral area canbe provided circumferentially around the entire sandwich structure, oronly on one or on individual sides on the sandwich structure.

However, in an alternative embodiment, the layer border or edge can alsolie freely in the core layer, without being joined or connected to theouter cover layer or to the inner cover layer. In the case of adiminishing core thickness, for example, a transition between atwo-piece core layer with an anchor layer and a one-piece core layer isthus achievable.

According to a further preferred embodiment, the anchor layer comprisesan outer anchor layer part, which points to or faces the outer coverlayer, and an inner anchor layer part, which points to or faces theinner cover layer and which preferably extends, at least in sections,parallel to the outer anchor layer part. The outer and inner anchorlayer parts extend transversely, preferably perpendicularly, to thethickness direction. Between the outer and inner anchor layer parts, thecore layer has a middle core layer section through which a middle groupof pins extends. The pins of the outer group are connected to the outeranchor layer part with the first end and to the outer cover layer withthe opposite second end. The pins of the inner group are connected tothe inner anchor layer part with the first end and to the inner coverlayer with the opposite second end. The pins of the middle group areconnected to the outer anchor layer part with a first end and to theinner anchor layer part with an opposite second end. With such atwo-piece construction of the anchor layer and three-piece constructionof the core layer, sandwich structures with core thicknesses greaterthan about 180 mm, namely up to about 270 mm, can also be reinforcedwith pins. Of course, the anchor layer can also have additional anchorlayer parts that subdivide the core layer into additional core layersections such that even greater core thicknesses can be spanned in thismanner.

Another aspect of the present disclosure relates to an aircraft orairplane with a fuselage and a wing. The wing extends between a wing tippointing or facing away from the fuselage and a wing root opposite thewing tip, with which wing root the wing is secured to the fuselage. Inthe area of the wing root, the wing comprises a sandwich structureaccording to one of the previously described embodiments. The wing ispreferably formed or constructed as a shell structure with a top orupper shell part and a bottom or lower shell part, wherein the top shellpart and/or the bottom shell part comprise(s) a sandwich structureaccording to one of the previously described embodiments in the area ofthe wing root. The outer cover layer can form an outer surface of thewing and the inner cover layer can point to or face the inner side ofthe shell structure or rather of the wing. Particularly in the area ofthe wing root, the wing, i.e., at least one of the shell parts of thewing, has a particularly large core thickness, so that pins are used inconjunction with an anchor layer for reinforcing the sandwich structurein this area, as was previously described.

In this regard, it is particularly preferred if the spacing or distancebetween the outer and the inner cover layers decreases from the wingroot towards the wing tip, i.e., the core thickness decreases towardsthe wing tip, because the loads decrease in this direction. Startingfrom the wing root, the anchor layer extends towards the wing tip, atleast as far as a location at which the spacing or distance between theouter and the inner cover layers is between 30 mm and 200 mm, preferably90 mm, depending on the density of the material of the core layer. Fromthis location on, where the core thickness becomes less than about 90mm, the pins can be used without an anchor layer because they are ableto extend from the outer to the inner core layer. The anchor layer canend in the area of the core layer between the outer and the inner coverlayer, without being connected to one of the cover layers. However, theanchor layer can also be secured to one of the cover layers and endthere.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present disclosure shall be explained inmore detail below, with reference to drawings. The drawing show in:

FIG. 1 a cross section of a first exemplary embodiment of the sandwichstructure according to the disclosure herein with a one-piece anchorlayer;

FIG. 2 a cross section of a second exemplary embodiment of the sandwichstructure according to the disclosure herein with a two-piece anchorlayer;

FIG. 3 a diagrammatic cross sectional view of an airplane or aircraftaccording to the disclosure herein with a sandwich structure accordingto the disclosure herein; and

FIG. 4 a detailed view of the wing root, configured as a sandwichstructure, of the aircraft or airplane from FIG. 3.

DETAILED DESCRIPTION

A first exemplary embodiment of a sandwich structure 1 according to thedisclosure herein is illustrated in FIG. 1. The sandwich structure 1 isformed in the shape of a shell or plate, which extends in a planeperpendicular to a thickness direction 3 and comprises a circumferentialperipheral or edge area 5. The sandwich structure 1 comprises an outercover layer 7, an inner cover layer 9 disposed opposite the outer coverlayer 7 in the thickness direction 3, and a core layer 11, which, asviewed in the thickness direction 3, is disposed between the outer andinner cover layers 7, 9 and connects them.

The sandwich structure 1 furthermore comprises a plurality of pins 13,which extend between the outer and the inner cover layers 7, 9, throughthe core layer 11. Further, an anchor layer 15 is provided between theouter and the inner cover layers 7, 9, which anchor layer 15 extendsperpendicularly to the thickness direction 3 and divides the core layer11 into an outer core layer section or portion 17 in abutment with theouter cover layer 7 and an inner core layer section or portion 9 inabutment with the inner cover layer 19. An outer group 13 a of pins 13extends through the outer core layer section 17 and an inner group 13 bof pins 13 extends through the inner core layer section 19, wherein thepins 13 of the outer group 13 a are fixed in the anchor layer 15 with afirst end 21 and in the outer cover layer 7 with an opposite second end23, and the pins 13 of the inner group 13 b are fixed in the anchorlayer 15 with the first end 21 and in the inner cover layer 9 with theopposite second end 23.

The outer cover layer 7, the inner cover layer 9, the anchor layer 15,and the pins 13 in the present exemplary embodiment are formed from afiber composite material, namely CFRP, and cured with each other inmonolithic fashion. The anchor layer 15 comprises a layer border or edge25 at which the anchor layer 15 is monolithically connected to the outerand the inner cover layers 7, 9, wherein in the peripheral or edge area5 of the sandwich structure 1, the layer border or edge 25 of the anchorlayer 15 is disposed between the outer and the inner cover layers 7, 9and is cured together with them in monolithic fashion. By the anchorlayer 15, in which the pins 13 are fixed or secured with their first end21, the sandwich structure 1 can be configured with a large corethickness without the pins 13 having to have a large length. Suchsandwich structures 1 with large core thicknesses can be used, forexample, in aircraft or airplane construction, particularly in thepressure bulkhead or in the wing in the area of the wing root, for rotorblades of wind power plants, for pressure tanks or containers, or forvehicles with larger dimensions, such as trains.

In FIG. 2 a second exemplary embodiment of the sandwich structure 1according to the disclosure herein is shown, which resembles the firstexemplary embodiment, so that corresponding features are designated withthe same reference signs.

The second exemplary embodiment of the sandwich structure 1 differs fromthe first exemplary embodiment, in that the anchor layer 15 comprises anouter anchor layer part 27 pointing to or facing the outer cover layer 7and an inner anchor layer part 29 pointing to or facing the inner coverlayer 9, wherein the outer and the inner anchor layer parts 27, 29 runor extend transversely to the thickness direction 3. Between the outerand the inner anchor layer parts 27, 29, the core layer 11 has a middlecore layer section or portion 31 through which a middle group 13 c ofpins 31 extends. The anchor layer 15 is thus divided into two anchorlayer parts 27, 29 running or extending transversely to the thicknessdirection 3 and approximately parallel to the cover layers 7, 9, betweenwhich parts the middle core layer section 31 is enclosed. The pins 13 ofthe outer group 13 a are fixed in the outer anchor layer part 27 withtheir first end 21 and in the outer cover layer 7 with their oppositesecond end 23. The pins 13 of the inner group 13 b are fixed in theinner anchor layer part 29 with their first end 21 and in the innercover layer 9 with their opposite second end 23. The pins 13 of themiddle group 13 c are fixed in the outer anchor layer part 27 with theirfirst end 21 and in the inner anchor layer part 29 with their oppositesecond end 23. Even greater core thicknesses of the sandwich structure 1are achievable with such a two-piece anchor layer 15, without having tolengthen the pins 13.

In FIGS. 3 and 4 an exemplary embodiment of an aircraft or airplane 33according to the disclosure herein is shown, that comprises a sandwichstructure 1 similar to that of FIG. 1; hence corresponding features aredesignated with the same reference signs.

As illustrated in FIG. 3, the aircraft or airplane 33 comprises afuselage 35 and a wing 37. The wing 37 extends between a wing tip 39pointing or facing away from the fuselage 35 and a wing root 41 oppositethe wing tip 39. The wing 37 is secured to the fuselage 35 at the wingroot 41. The wing 37 is formed as a shell structure 43 with a top orupper shell part 43 a and a bottom or lower shell part 43 b. As can bediscerned from the section illustrated in FIG. 4, the top shell part 43a is configured in the area of the wing root 41 as a sandwich structure1 similar to that of FIG. 1. The sandwich structure 1 comprises an outercover layer 7, an inner cover layer 9, and a core layer 11 providedbetween the cover layers 7, 9. The sandwich structure 1 furthercomprises an anchor layer 15 running or extending between the outer andthe inner cover layers 7, 9 in the area of the core layer 11, whichanchor layer 15 divides the core layer 11 in the area of the wing root41 into an outer core layer section 17 in abutment with the outer coverlayer 7 and an inner core layer section 19 in abutment with the innercover layer 9. The sandwich structure 1 further comprises a plurality ofpins 13, of which an outer group 13 a extends through the outer corelayer section 17 and an inner group 13 b extends through the inner corelayer section 19. The pins 13 of the outer group 13 a are fixed in theanchor layer 15 with their first end 21 and in the outer cover layer 7with their second end 23, and the pins 13 of the inner group 13 b arefixed in the anchor layer 15 with their first end 21 and in the innercover layer 9 with their second end 23.

In this manner, it is possible to reinforce the core layers 11 of theshell structure 43 with a thickness as great as about 180 mm at the wingroot 41 with pins 13, without the pins 13 exceeding a length of 90 mm.As can be discerned in FIG. 4, the spacing or distance between the outerand inner cover layers 7, 9 decreases from the wing root 41 towards thewing tip 39, so that at a location 45 at which the spacing or distancebetween the outer and inner cover layers 7, 9 is about 90 mm or less, ananchor layer 15 is no longer needed for establishing a pin connectionbetween the two cover layers 7, 9 without having to use pins 13 longerthan about 90 mm. Starting from the wing root 41, the anchor layer 15thus extends towards the wing tip 39 at least as far as a location 45(but not beyond this location 45 in the present exemplary embodiment) atwhich the spacing or distance between the outer and inner cover layers7, 9 is 90 mm.

While at least one exemplary embodiment of the present invention(s)herein is disclosed herein, it should be understood that modifications,substitutions and alternatives may be apparent to one of ordinary skillin the art and can be made without departing from the scope of thisdisclosure. This disclosure is intended to cover any adaptations orvariations of the exemplary embodiment(s). In addition, in thisdisclosure, the terms “comprise” or “comprising” do not exclude otherelements or steps, the terms “a” or “one” do not exclude a pluralnumber, and the term “or” means either or both. Furthermore,characteristics or steps which have been described may also be used incombination with other characteristics or steps and in any order unlessthe disclosure or context suggests otherwise. This disclosure herebyincorporates by reference the complete disclosure of any patent orapplication from which it claims benefit or priority.

1. A sandwich structure comprising: an outer cover layer; an inner coverlayer disposed opposite the outer cover layer in a thickness direction;a core layer, which, as viewed in the thickness direction, is disposedbetween the outer and the inner cover layers and connects them; and aplurality of pins which extend between the outer and the inner coverlayers, through the core layer; an anchor layer between the outer andthe inner cover layers, anchor layer extending transversely to thethickness direction and dividing the core layer, at least in areas, intoan outer core layer section in abutment with the outer cover layer andan inner core layer section in abutment with the inner cover layer; anouter group of pins extending through the outer core layer section andan inner group of pins extending through the inner core layer section;and the pins of the outer group being connected to the anchor layer withtheir first end and to the outer cover layer with their opposite secondend, and the pins of the inner group being connected to the anchor layerwith their first end and to the inner cover layer with their oppositesecond end.
 2. The sandwich structure according to claim 1, wherein theouter and the inner cover layers, the anchor layer, and the pins areformed monolithically with each other from a fiber composite material.3. The sandwich structure according to claim 1, wherein at a layerborder, the anchor layer is monolithically joined to the outer and/or tothe inner cover layer(s).
 4. The sandwich structure according to claim3, wherein the sandwich structure has a peripheral area at which thecover layers are monolithically joined to one another, wherein at theperipheral area of the sandwich structure, the anchor layer ismonolithically joined with its layer border to the outer and inner coverlayers.
 5. The sandwich structure according to claim 1, wherein theanchor layer comprises an outer anchor layer part pointing to the outercover layer and an inner anchor layer part pointing to the inner coverlayer, wherein the outer and inner anchor layer parts run transverselyto the thickness direction, wherein between the outer and inner anchorlayer parts, the core layer has a middle core layer section throughwhich a middle group of pins extends, wherein the pins of the outergroup are connected to the outer anchor layer part with their first endand to the outer cover layer with their opposite second end, wherein thepins of the inner group are connected to the inner anchor layer sectionwith their first end and to the inner cover layer with their oppositesecond end, and wherein the pins of the middle group are connected tothe outer anchor layer part with their first end and to the inner anchorlayer part with their opposite second end.
 6. An aircraft comprising afuselage and a wing, wherein the wing extends between a wing tippointing away from the fuselage and a wing root opposite the wing tip,with which wing root the wing is fastened to the fuselage, wherein thewing is formed as a shell structure with an upper shell part and a lowershell part, and wherein the upper shell part and/or the lower shell partcomprise a sandwich structure in an area of the wing root, the sandwichstructure comprising: an outer cover layer; an inner cover layerdisposed opposite the outer cover layer in a thickness direction; a corelayer, which, as viewed in the thickness direction, is disposed betweenthe outer and the inner cover layers and connects them; and a pluralityof pins which extend between the outer and the inner cover layers,through the core layer; an anchor layer between the outer and the innercover layers, anchor layer extending transversely to the thicknessdirection and dividing the core layer, at least in areas, into an outercore layer section in abutment with the outer cover layer and an innercore layer section in abutment with the inner cover layer; an outergroup of pins extending through the outer core layer section and aninner group of pins extending through the inner core layer section; andthe pins of the outer group being connected to the anchor layer withtheir first end and to the outer cover layer with their opposite secondend, and the pins of the inner group being connected to the anchor layerwith their first end and to the inner cover layer with their oppositesecond end. The aircraft according to claim 6, wherein spacing betweenthe outer and inner cover layers decreases from the wing root towardsthe wing tip, and wherein starting from the wing root, the anchor layerextends towards the wing tip at least as far as a location at which thespacing between the outer and inner cover layers is between 30 mm and200 mm.